The present disclosure relates to a fixing device fixing a toner image on a sheet and an image forming apparatus including the fixing device.
In response to a request for saving energy and shortening a warm-up time, a fixing device having a small heat capacity is developed. For a fixing device having a small heat capacity, a flexible fixing belt to be electromagnetically heated by an exciting coil is sometimes used. A pressing member is pressed against the fixing belt to form a pressing area between the pressing member and the fixing belt. When the pressing member is rotated, the fixing belt is driven to be rotated, and a sheet passes through the pressing area. At this time, a toner image transferred on the sheet is heated and pressed to be fixed on the sheet. Inside the fixing belt, a belt guide is disposed so as to face the exciting coil at a position opposing to the pressing area. The belt guide comes into contact with an inner circumferential face of the fixing belt to support the fixing belt. Such a belt guide makes it possible to reduce the heat capacity of the fixing belt.
In such a fixing device, when the fixing belt is rotated, the pressing member and the belt guide are slid with respect to the fixing belt. If sliding load of the pressing member and the belt guide is large, the fixing belt may be slipped to cause heating failure and conveying failure.
Especially, if a pressure of the pressing area is changeable, when the pressure is lowered, since a driving force of the fixing belt is lowered, these failure are easily occurred.
The fixing device is sometimes provided with a separating mechanism in which a heating member (the belt guide) disposed to come into contact with the inner circumferential face of the fixing belt is separated with respect to the fixing belt. By separating the heating member from the fixing belt, a heating condition of the heating belt can be finely adjusted.
However, if the heating member is separated from the fixing belt, a rotating orbit of the fixing belt becomes unstable or changes. Then, a distance between the exciting coil and the fixing belt is changed, and then a heating efficiency of the fixing belt may be lowered or a conveying failure may be occurred at an inlet for the pressing area.